Almost missed it as the map location is wrong. It is by the roundabout, to the right after the border zone down an alleyway behind the obvious transport place. Note: the immigration hase moved closer to the border, it's no longer behind the immigration office.
Staff were nice and put me on a motorbike to catch it. The van was comfortable but seatbelts didn't seem to work. Fast and scary driving but still 2 hours late.
There was a short stop at their siem reap depot with toilets. There was a 30 minute stop at a service station with very good toilets, a convenience store and cafe and a lakeside restaurant. The food was all khmer and i didn't find anything vegetarian in the restaurant. Ok coffee though.
The driver spoke English enough to tell me how long we would stop etc. And if requested he could find another toilet stop, though obviously this would make things slower.
Overall, having used a number of other travel companies in Cambodia i would say this is a good one.